The right arm began to fail…gradually progressive weakness came on, just like the leg, but especially in the thumb and forefingers, and she experienced a difficulty in holding things. The difficulty increased so that she dragged the right leg, which felt heavy and cold, and it commenced to waste. 5 More aggressive and classical MND is referred more quickly to neurologists 6 thus, true mimics (and also some of the chameleons) tend to be slowly progressive disorders and time is often the neurologist's most valuable diagnostic tool. The most robust marker of prognosis is still the interval from symptom onset to definitive diagnosis, the average for which has remained approximately 1 year, 4 around a third of the median survival from symptom onset. 3 Diagnostic delay in MND due to the insidious nature of disease onset and referral from primary care to inappropriate specialists are to a large extent beyond the influence of the neurologist ( figure 1).
There is no diagnostic test for MND, and the quest for biomarkers is ongoing. Conversely, significant distress can arise from avoidable diagnostic delay and this may permanently erode confidence in onward management. The diagnosis of MND is only very rarely reversed in favour of a treatable disorder and, in our experience, the reaction of the patient in this situation is one of relief not hostility. Might we, as neurologists, also occasionally succumb to the fear of just not wanting to get it wrong in a speciality where diagnostic precision is so highly prized? Most MND mimic disorders are equally irreversible, though there are still implications for the accurate counselling of patients and care-planning, meaning it is entirely appropriate to pursue these vigorously where clinically indicated. It is easy to understand why the neurologist might wish to put off conveying the diagnosis and to undertake every possible investigation in the pursuit of treatable alternatives. The best test of a physician's suitability for the specialized practice of neurology is not his ability to memorize improbable syndromes but whether he can continue to support a case of motor neurone disease, and keep the patient, his relatives and himself in a reasonably cheerful frame of mind. The Oxford neurologist W Bryan Matthews perfectly articulated the unique challenge of MND for the clinician: 1 Thus, the news of relentlessly progressive limb weakness, likely involvement of speech, swallowing and breathing, dramatic shortening of life expectancy, but no significant disease-modifying therapy, is as surprising as it is devastating for the patient and their family. There can be few worse tasks facing the neurologist than giving the diagnosis of motor neurone disease (MND), a condition which is not well understood by the general public.
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